This invention relates generally to methods for producing adhesive bonds between a substrate and a polymer. More particularly the methods of this invention relate to enhancing the silane coupling bond between a substrate and polymer. Furthermore, the methods of the invention are especially suited for dental application in the restoration of teeth.
Heretofore the restoration of anterior teeth, particularly in children exhibiting decayed, eroded, or fractured anterior primary teeth, has involved fitting stainless steel crowns or caps over the damaged teeth. While the stainless steel crowns are well suited for structural and functional restoration of primary teeth, they are unaesthetic. For example, children fitted with such stainless steel crowns are often singled out by their peers as having "funny silver teeth". Aesthetic alternatives, however, principally the polycarbonate resin crowns, are not favored because such crowns exhibit poor wear resistance, inadequate retention, and susceptibility to cracking in service.
It therefore is a desirable approach to the restoration of teeth to combine the functional properties of the stainless steel crown with the aesthetics presented by the polymeric crowns. One such approach which has been suggested is to veneer the steel crown with a thin layer of polymeric resin. Although veneering has been successfully employed for a number of years for the restoration of natural teeth to mask defects such as developmental anomalies, and tetracycline and fluorosis stains, a durable stainless steel-polymer veneer has not been developed.
In veneering natural teeth, the damaged teeth are isolated, cleaned, etched with phosphoric acid, and dried. A composite restorative resin is applied to the etched surface and cured. Mechanical interlocking of the resin with the etched surface of the tooth enamel results in an adhesive bond strength which is sufficient to accomplish a restoration having acceptable clinical durability. Unfortunately, stainless steel is not amenable to a similar approach because retentive etch pits cannot be adequately developed in steel by acid etching.
Alternative approaches to produce a durable stainless steel-polymer veneer crown have involved chemical bonding techniques. The widely used industrial adhesive agents such as epoxy resins, phenol-formaldehyde resins and acrylic resins have been employed in the past to adhere polymers to substrates. Unfortunately the secondary chemical bonds formed between the substrate and polymer provide weak structural construction relative to the structural stresses presented to the crowns when in service. Not only are the veneered products subject to cracking, flaking and fracture, the veener composite may exhibit undesirable permeability to gases such as water vapor, and liquids, thereby allowing further weakening of the veneer structure.
Other approaches to combine functional strength and aesthetics include pigmenting the steel crowns. For example, commercial crowns were at one time available with white pigmented layers. These crowns, however were not successful because of the rapid loss of the pigment coating after oral placement.
A more recent attempt to produce an aesthetic-functional composite involves a two-step chairside procedure. First the damaged tooth is sized with a stainless steel crown. Next the sized crown is removed and then subjected to laboratory treatment to construct a porcelain coating. Although a structurally and aesthetically durable crown is achieved, these merits must be weighed against the disadvantages of additional laboratory costs to produce a porcelain coating compared to a polymeric coating, and extended chair time.
As can be appreciated from the foregoing, the need still remains for a dental crown which combines the structural strength of steel and the aesthetics of a polymer resin. It is therefore a feature of the present invention to provide a methods for producing strong adhesive bonds between a substrate and polymer resin.